Electroplating is a well-known process, as is development of photographic materials. The uniformity and reproducibility of development is dependent on a number of factors including temperature, chemical activity and agitation of the developer solution. Automated processors controlling various aspects of these factors are commonly used for developing photographic elements. Processors use well-known technology to carefully control parameters of the development process. Temperature controls permitting limitations in temperature variations to .+-.0.5.degree. C. (.+-.1.degree. F.) are routine. In addition, some degree of movement of the processing fluid (a.k.a. agitation) is important and various methods are available for creating this movement within the processing liquids. Among such available methods are roller movement and recirculation of the bath liquid. The chemical activity of the processing bath is maintained through an automated replenishment process.
It is desirable to reduce the amount of materials used in the processing of photographic film from both an economic and ecological point of view. While a square-meter, dry sheet of silver halide imaging material can imbibe up to 40 milliliters of developer fluid, inefficient fluid usage occurs in known developers via excessive leakage from the chamber and gradual deterioration due to oxidation. Manufacturers of newer silver halide developers have attempted to optimize the processing of silver halide materials as efficiently as possible using the least amounts of processing chemicals, while assuring no sacrifice in the high quality of performance that is expected of such materials.
Maintenance of the appropriate level of chemical activity is an important aspect of the development process which assures consistent performance for the product. During development, components of the developer are depleted as reactants are consumed and reaction products are formed. Of particular note are the depletion of hydroquinone and hydroxide ion as reactants and the ultimate formation of hydroquinone monosulfonate or hydroquinone disulfonate and a bromide ion as reaction products. The depletion of the reactants and formation of the reaction products lead to deterioration of the processing bath's capability to develop further images. The leaching of materials from the photographic element can also lead to a deterioration of development quality. It is the role of agitation to remove the reaction products from the surface of the photographic medium and to provide fresh chemistry to the surface of the medium to assure continued development of the medium by diffusion into the layer where the image-forming reaction is occurring. It is the role of replenishment to provide a continued supply of reactants and dilution of the reaction products to maintain the overall chemical activity for the processing bath.
The replenishment requirements and sustained capacity of a processing bath to develop film are determined by a number of factors including the silver content of the film, the degree to which the silver halide crystals are converted to image silver (i.e., the usage rate) and the formulation of the developer. A goal is to achieve a steady state in which the replenishment maintains the activity of the bath at a constant level to provide consistent and reproducible development results. Under-replenishment, i.e., insufficient replenishment, leads to deterioration of the processing bath with a decreased processing activity. A result of under-development is insufficient image (low density), low contrast and eventually exhaustion where there is little or no development. Over-replenishment, on the other hand, can lead to a condition in which the activity of the bath becomes excessive and results in over-development, excess image (high density), high contrast and excessive fogging (Dmin) of the film. Conventionally, the recommended practice to provide consistency has been to use a very large reservoir of reactants, which is wasteful with respect to the chemicals being used.
A distinction must be made between the developer in the processing bath and the developer in the replenisher, which is added to maintain the activity of the bath. The developer within the bath, also known as the working developer, may be derived from the replenisher. However, the working developer in an automated processor includes reaction byproducts as well as a reduced level of reactants when compared to the replenisher. In a steady state situation, the developer and reaction products remain at a constant level, accumulating reaction products and depleting reactants during development, while replenishment supplies fresh reactants and dilutes the reaction byproducts. At a proper replenishment rate, the system maintains an approximately steady state balance providing consistent development for the photographic film. The use of a replenisher solution for the development of a film in a replenisher would normally result in an over-developed image, as the replenisher solution is a stronger developing bath than the seasoned or working developer bath. It is, however, common in the art to prepare a working developer bath from a replenisher by either diluting the replenisher solution, adding some reaction products, e.g., bromide, running some exposed film through without replenishment, or some combination to suppress the excess activity of the replenisher and bring it to the level of the working developer.
To assist in maintaining consistent chemical activity, it is common practice that automated processors have a developer bath with a significant volume of liquid, e.g., 20 liters or more. These are generally called "deep tank processors". Deep tank processors have provided the highest throughput rate and have provided a buffering capacity for the developer bath which contributes to the consistency of the process.
Disadvantages of deep tank processors, however, are significant. First and probably foremost, the use and eventual disposal of a large volume of processing fluid is ecologically undesirable. This disadvantage is accentuated when the operator is caused to dump a large volume of fluid due to incorrect mixing or due to fluid contamination. Second, the large volume is economically undesirable to purchasers. Third, a significant period of time is required to heat the large volume to the desired operating temperature.
Shallower tanks or reduced volume tanks have been made commercially available to address the disadvantages of the deep tank processors. However, they have not met with significant acceptance. One of the primary reasons for lack of general acceptance is that low-volume processors traditionally have either not provided the output requirements (productivity for processing imaging material, i.e., throughput rate) or not provided the consistency of performance (development uniformity without scratching, pressure marking, or creating other artifacts in the imaging material) that are provided by deep tank processors.
U.S. Pat. No. 5,168,926 describes a processor with partitioned processing chambers designed to use a smaller volume and provide proper development. This patent not only reports the use of a lower fill volume but also a reduced usage rate for the replenisher (milliliters per square meter).
WO Patent No. 93-00612 defines an apparatus for photographic processing in a low-volume tank and teaches the importance of agitation. It states that in low-volume processors, the confines of the tank restrict adequate agitation and, therefore, access of fresh processing solution to the film surface. The patent defines means to assure the access of fresh processing solution to the film surface.
In EPO Patent No. 410322, the chemistry is dispensed directly onto the film for processing. Such imbibement processing requires that the chemistry be formulated so there are sufficient reactants in the volume imbibed to assure full development of the image. EPO Patent No. 410322 requires a minimum of two dispensings of the developer formulation. However, the material dispensed does not become part of the developer in a processing tank.
U.S. Pat. No. 5,059,997 is an example of a low-volume tank which attempts to effectively limit contact of the solution with air and thereby reduce degradation of the developer by oxidation.
U.S. Pat. No. 5,266,994 is example of a low-volume processing tank which includes a plurality of fingers which are intended to distribute processing solution over the surface of the material being processed.
As previously noted, chemical activity is maintained by replenishment in which fresh chemistry is added at a rate commensurate with the quantity (area) of film processed, or more properly, the quantity of silver image that is developed. For most processes in the industrial black and white markets, e.g., the medical and graphic arts areas, the prescribed replenishment rate is usually about 450 milliliters of the replenishment chemistry per square meter of film processed, with assumptions that the development process develops about 50% of the available silver and that the silver coating weight of the materials used is in the range of 3 to 4 grams per square meter of film processed. In processes where the preponderance of film going through the process has a different silver coating weight or the balance of silver converted to image is significantly different than 50%, the recommended replenishment rate is normally adjusted to compensate for the differences.
As an example, for 50% imaged or exposed films, the data sheets for one company's products generally recommend 39 milliliters per square foot for 50% imaged silver halide photographic film (53 milliliters per square foot for 75% imaged film). The 39 milliliters per square foot is equivalent to 420 milliliters per square meter. Some use as low as 29 milliliters per square foot can be envisaged, which is equivalent to 312 milliliters per square meter. Other uses in the range of 22 to 35 milliliters per square foot for 50% imaged film, which is equivalent to 235 to 375 milliliters per square meter, have been recommended. In this regard, it should be noted that while a number of patents refer to the benefits of low-volume processor tanks and the resultant reduction in chemistry usage, such references are always to the tank volumes and the requirements associated with filling or dumping such tanks. None of the references appear to refer to the requirements of replenishment other than that replenishment conventionally used to maintain the process over an extended period of time and to provide extended usage of developer materials.
One known, commercially available processing chemistry formulation achieves a reduction in the volume of replenishment chemistry used. However, the volume reduction does not translate to an equivalent reduction in the material usage, e.g., the absolute amount of hydroquinone (HQ) used. While using this formulation allows for a reduction of the replenishment volume from 0.450 to 0.125 liters per square meter of film developed, the concentration of the hydroquinone used in the processing bath is increased by 1.5 to 2 times that of a normal concentration (from 50 to 80, but nominally 65 grams HQ per liter to approximately and nominally 113.8 grams HQ per liter). As a result, the usage of HQ is only reduced from 29.3 grams per square meter (at a 50% image) to about 14.3 grams HQ per square meter. This usage still results in a significant waste of HQ. (Approximately 1 gram of HQ is all that is used per square meter of film developed when the processing fluid includes 65 grams HQ/liter, the film includes 4 grams Ag/square meter of film developed, and the film is 50% imaged.)
A need remains for an apparatus and method which a) minimize the use of the chemicals involved (via the reduction of fluid loss, efficient usage of the chemicals, and/or the reduction of oxidation), b) minimize the scratching and/or pressure marking of the material while being transported through the apparatus, and c) provides adequate development uniformity and productivity. This need is particularly felt for processing imaging materials, such as photographic films, proofing plates, and diffusion transfer-type imaging materials, particularly wider imaging materials.
Because many of the deficiencies of the deep-tank developers are shared by the known electroplating apparatuses, a need also exists for an electroplating apparatus and method which involves: a) minimal usage and loss of the electroplating fluid, yet relatively high fluid flow rates, b) efficient use of space (footprint), and c) good control of the temperature of the electroplating fluid.